A retired Los Angeles County sheriff’s commander who played a role in exposing abuses inside the agency’s jails announced Wednesday that he is going to challenge Sheriff Lee Baca in next year’s election.

Bob Olmsted promised to clean up a department that he says has been beset by scandal because of mismanagement and cronyism by Baca.

Baca, who has been sheriff for about 15 years, enters his relection campaign amid several scandals. Over the weekend, Supervisor Gloria Molinapublished a letter in The Times blasting Baca and expressing disappointment that “not one challenger has stepped forward to rescue” the Sheriff’s Department.

Two others have entered the race. But Olmsted is considered the most serious challenger to Baca, who has high name recognition and significant fundraising resources.

Olmsted, 62, was one of the first sheriff’s officials to break rank with his old boss. In 2011, he went public with his criticisms of the four-term sheriff, telling The Times that he warned Baca about deputies using excessive force against inmates but was ignored until the problems grew into a scandal.

Olmsted’s public statements contradicted Baca’s claims that he had been kept in the dark by his top aides about jailhouse problems.

Olmsted also commissioned internal audits raising alarms about jailer brutality, nearly two years before Baca acknowledged that it was a problem.

The documents contained disturbing evidence of misconduct in the jails, including cases in which deputies used unnecessary force, then escaped punishment because of shoddy investigations by supervisors.

One of the reports audited more than 100 violent encounters with inmates and found that deputies crafted narratives “dramatized to justify” force. In some cases, the jailers purposely delayed using weapons that could end fights, like pepper spray and stun guns, “to dispense appropriate jailhouse 'justice,’ ” the report said.

A blue ribbon commission later launched by the county to examine problems in the jails relied on those internal reports to make its case that excessive force was pervasive.

Before Olmsted went public with his criticism of the agency’s management, he was a source for an ongoing Times investigation of allegations of abuse and other jailer misconduct. He recently granted the Times permission to disclose his role as a source.

Olmsted was with the department for more than three decades. He rose to the rank of commander and was responsible for overseeing the agency’s most beleaguered lockups.

After the jail abuse scandal broke in 2011, Baca sought Olmsted's advice for fixing the problems and asked him to come out of retirement and temporarily work on the department's reform efforts. Olmsted declined.

When Olmsted went public with his criticisms against Baca, the sheriff called him a “very strong and competent commander.” But he faulted Olmsted for not fixing the jail issues himself.

“He doesn't have to ask permission to solve the problem,” Baca said at the time.

Sheriff’s officials later launched an investigation that they said was aimed at determining if anyone stopped Olmsted from correcting the problems he had seen with excessive force and aggressive jailer cliques. But Olmsted said at the time that the investigation was a “witch hunt” intended to scapegoat him, so he stopped cooperating.

Among the problems examined during that inquiry was the discovery that a large number of force packages — files used to keep track of clashes with inmates and ensure they are within policy — disappeared. The investigator on the case said that the lost reports went back years, spanning the tenures of three captains, including Olmsted.

Baca has faced a string of scandals in recent years. The FBI has been investigating abuse and other deputy misconduct in his jails. In a separate investigation, federal authorities found that Baca’s deputies in the Antelope Valley harassed and intimidated blacks and Latinos. In addition to the federal investigations, Baca had been under fire for questionable hires, giving special treatment to friends and supporters, and the existence of aggressive, unsanctioned deputy cliques within the agency's ranks.

Despite these problems, political experts have said knocking the four-term sheriff from his post will be a challenge.

Baca is well-known within the county and has drawn support from a diverse set of ethnic groups and community leaders. He has gained a reputation for progressive law enforcement views, such as helping the homeless and providing education for jail inmates. He also has already lined up a string of heavyweight endorsements.

According to the Olmsted campaign’s chief strategist, John Thomas, paperwork that will allow Olmsted to start fundraising will be filed Wednesday. Thomas said he expects to announce endorsements within days.

The campaign’s motto is “Olmsted Instead.”

“Voters deserve a Sheriff’s Department they can be proud of. I’m running for sheriff to restore integrity,” Olmsted said in a press release.

A Web ad was also released Wednesday featuring the former commander and a number of retired sheriff’s officials.

“He spoke up when other people were afraid to,” one former official says in the ad. “And that’s the kind of man you need for sheriff.”

The only other definite opponents Baca faces are a little-known L.A. police supervisor, Lou Vince, and a retired sheriff's lieutenant, Patrick Gomez, who has run two failed campaigns. Paul Tanaka, the controversial undersheriff whom Baca recently pressured to step down, is considering a run.